<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    .main{
        height: 200px;
        background: greenyellow;
        margin-left: 200px;
        margin-right: 200px;
    }
    .right {
        float: right;
        width: 200px;
        height: 200px;
        background: red;
    }
    .left {
        float: left;
        width: 200px;
        height: 200px;
        background: red;
    }
</style>
<body>
  <div class="container">
      <div class="left"></div>
      <div class="right"></div>
      <div class="main"></div>
  </div>  
</body>
</html>